1. Field of the Invention
This invention relates to a method for preparing the surface of a pyrotechnic composition for coating, especially those propellants suitable for use in inflating an inflatable device, such as a vehicle safety restraint.
2. Description of the Prior Art
Various pyrotechnic propellants have been prepared for generating a gas upon combustion in order to inflate an air bag or similar safety restraint in a vehicle so as to restrain movement of an occupant in the event of a sudden deceleration of the vehicle, such as caused by collision. In order to be employed as a pyrotechnic gas generating composition for inflatable occupant restraints, several criteria must be met. The pyrotechnic must be capable of producing non-toxic, non-flammable and essentially smokeless gases over a wide variety of temperatures and other environmental conditions. The gases that are generated must be totally ignited at a sufficiently low temperature so as not to destroy the restraint or injure the occupant. The pyrotechnic must also be safe to handle and must be capable of generating a substantial amount of gas within a very short period of time, e.g., less than about 100 milliseconds.
In order to achieve total ignition and combustion of the pyrotechnic formulation, various ignition enhancers can be used. Although the ignition enhancer can be admixed with the pyrotechnic material before the material is pressed into pellets it is preferred to first prepare the pyrotechnic pellets and subsequently apply the ignition enhancer as a coating. See for example co-filed application entitled, Ignition Enhancer Coating Compositions For Pyrotechnic Propellants, Inventors E. F. Garner and B. K. Hamilton, Attorney's Docket No. 2000-610, and incorporated herein by reference.
An ignition enhancer coating mix, and techniques for its application, require the solution of several problems, one of which is providing adequate adhesion of the coating to the propellant surface so that the coating can withstand the rigors of an automobile environment. In general, adhesion of the coating to the pellet can be a problem owing to the fact that the pyrotechnic propellant material is formulated from a variety of materials and mixed with a pressing aid such as Teflon, stearic acid, etc. These materials and pressing aids can have a slick deposit on the surface of the pellet, thereby making the application of a coating difficult.